1. Field of the Invention
The present invention relates to optical communication equipment and, more specifically but not exclusively, to signal processing in coherent optical transmission systems.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
The next-generation of optical communication systems is being designed for relatively high data-transmission rates, e.g., higher than about 100 Gbit/s per channel. At these rates, the effects of chromatic dispersion (CD) and polarization-mode dispersion (PMD) significantly degrade the transmission performance of optical fiber links. Since practical implementation of dispersion compensation in the optical domain is relatively expensive, various digital-signal-processing (DSP) techniques, such as orthogonal frequency division multiplexing (OFDM), are used to mitigate the adverse effects of CD and PMD on signal transmission. However, one problem with optical OFDM is that it requires relatively sophisticated digital signal processing not only at the receiver, but also at the transmitter. In addition, optical OFDM has a relatively high peak-to-average power ratio (PAPR), which adversely affects the hardware cost by imposing rather stringent constraints on modulation and power-amplifier nonlinearities.